LONDON, Aug 4 (Reuters) - Sibanye-Stillwater

has asked the United States to consider imposing a tariff on

Russian palladium imports to support the long-term viability of

U.S. supplies, in a move that could increase volatility in

palladium prices.

The petition filed by Johannesburg-based Sibanye-Stillwater

adds another layer of uncertainty to prospects for platinum

group metals (PGMs) after a rally in prices so far this year due

to lower first-half production in South Africa and thin

liquidity in the spot market.

"We believe that Russian palladium imports are being sold

below market prices due to various factors, beginning primarily

after the Russian invasion of Ukraine in 2022,"

Sibanye-Stillwater's Chief Executive Neal Froneman said in a

statement on the company's website dated July 31.

"Obtaining relief from dumped and subsidised Russian imports

will give Sibanye-Stillwater, its employees, and the entire U.S.

PGM industry, an opportunity to compete on a more level playing

field," he added.

A final decision on the petition is likely within 13 months.

Russia's Nornickel, the world's largest palladium producer

with a 40% share of global mined output, declined to comment.

Sibanye-Stillwater, which has production assets in South

Africa and the United States, suffered its second consecutive

full-year loss last year after writing down $500 million of its

U.S. palladium assets amid low prices.

Spot palladium prices are up 31% so far this year,

and the outlook for the rest of the year is positive for miners:

analysts forecast in a Reuters poll in July that the palladium

price would rise in 2025 for the first time in four years, aided

by platinum's rally.

"Although placing duties on Russian metal would not

necessarily impact the market balance of palladium, it could

result in the re-routing of global physical metal flows, leading

to price volatility," analysts at Heraeus said.

Russia and South Africa are the top suppliers of palladium

to the United States, according to the Trade Data Monitor. For

Russia, China is the second largest buyer of the metal after the

United States.

Russian palladium imports to the U.S. increased 42%

year-on-year to more than 500,000 troy ounces in January-May,

according to Heraeus.

PGMs, used widely to clean exhausts in gasoline vehicles,

have so far avoided both U.S. sanctions imposed on Russian

companies over the Ukraine war and any import tariffs announced

by President Donald Trump.